The objective of the proposed research is to construct a prototype narrow-bandwidth x-ray source for mammography using a thin, efficient hybrid radiator driven by a relativistic electron beam of moderate energy and current. The high x-ray yield (photons/electron) of the source permits the use of modest electron-beam currents, preventing thermal damage to the radiator itself. The radiator is thin, permitting the electron beam to pass through it many times, thereby proportionally increasing the emitted x-ray flux. Since the source is inherently collimated and quasi-monochromatic, it will produce higher quality radiographic images while lowering the dose to the patient. Phase I experiments have demonstrated intense quasi-monochromatic x-rays in the range optimum for mammography (15 to 25 keV). Calculations of the x-ray yield and the average current passing through the radiator have demonstrated that there is adequate flux for imaging. The research will proceed by improving the design of the thin hybrid radiator and experimentally demonstrating its feasibility by producing images of inanimate phantoms. The potential for successful development of the prototype imaging system is very high because our Phase I research has already experimentally demonstrated, both electron recycling and narrow bandwidth, tunable x-ray generation. These results indicate that a high quality mammogram can be generated in less than 3 seconds.